Coal pulverizers are typically used to grind, dry and classify raw chunks of coal into fine solids which can be fluidized and fed, for example, to burners used in conjunction with industrial or utility boilers or furnaces. As is known to those skilled in the art, several different types of coal pulverizers, or coal mills, exist today, including those known by the designations “E” or “EL.”
EL type pulverizers are ball-and-ring (or ball-and-race) type pulverizers which employ the ball-bearing principle to grind the coal. EL pulverizers were first produced in the early 1950's. Conventional E and EL pulverizers use two vertical axis, horizontal grinding rings, and a set of balls placed between the grinding rings. The lower or bottom grinding ring rotates through connection to a rotating, vertical main shaft, while the upper or top grinding ring remains stationary and is spring loaded to create grinding pressure.
The coal may be ground by contact with the upper and lower grinding rings and balls (collectively, the grinding elements). The lower and upper grinding rings create a matching track that engages the balls. The force from the upper grinding ring pushes the balls against the coal layer on the lower grinding ring. The grinding rings and the balls are made of abrasion resistant alloys and comprise the major wear parts of the mill. Ground coal is swept from the grinding zone defined by the grinding rings and the balls by air for final particle size classification and subsequent pneumatic transport to one or more coal burners. Further details of EL type pulverizers are discussed in Chapter 12 of “Steam/Its Generation and Use,” 40th Edition, Stultz and Kitto, Eds., Copyright 1992, The Babcock & Wilcox Company, which is hereby incorporated by reference as though fully set forth herein.
EL mill top grinding rings have historically been loaded by using up to six single load coil springs. Measurement data necessary for spring adjustments require the pulverizer to be taken off line and opened to allow access to the grinding elements. Spring adjustments are then made manually with a wrench on a screw adjustment. Accordingly, it is desirable to provide a system for adjusting the load springs which reduces the time and complexity in adjusting the load springs to accommodate for wear on the grinding balls.